Electronic products, such as computers or servers, are becoming thinner, causing their inner spaces to become smaller. For example, in a server, electronic components, such as hard disks, occupy most of the inner space and cause high airflow resistance. Therefore, when a cooling fan is operating, the cooling fan must create a high speed airflow in the server to overcome the airflow resistance. However, the operating cooling fan may then cause high-frequency vibration noise and reduce hard disk drive reading and writing efficiencies.